Cross coil instrument with a predefined characteristic

ABSTRACT

The present invention relates to the visual representation of an input value, and provides an instrument, which can be given any predefined characteristic of its visual display. Cross-coil instrument is provided, said cross-coil instrument comprising a driver for the instrument characterized in that it further comprises a digital input terminal, a predetermined characteristic of the instrument stored as a map of input/output values in a digital memory and a microprocessor, said input value being a value represented visually by the cross-coil instrument, said output value being the value applied to the cross-coil instrument to visual represent the input value.

This application claims the benefit of Danish Application No. 2002 00535filed Apr. 10, 2002 and PCT/DK03/00242 filed Apr. 10, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to a cross-coil instrument with apredefined characteristic as well as a method for giving the instrumentsuch a characteristic. More particularly the invention relates to across-coil instrument with a highly linear characteristic or acharacteristic with linearity with different constants in differentareas of the scale.

Conventional instruments with a highly linear characteristic aremanufactured with moving-coil instruments. This is disadvantageousbecause moving-coil instruments with a highly linear characteristic areexpensive. Furthermore, the indicating device of a moving-coilinstrument is limited in rotation, because wires are connected to therotating device. Another drawback on moving-coil instruments is that theindicating device has to be light-weight. This makes the instrumentsensitive to static electricity and makes it vulnerable to mechanicalstress, which can change the calibration of the instrument.

Conventional cross-coil instruments are used for various measuring anddisplay purpose. For instance, for process-indication, measuring thelevel of liquid or temperature as rudder angle-indicators or else as avoltmeter and an ammeter. A cross coil type instrument includes amovable permanent magnet around which a plurality of coils arecross-arranged. Currents based on a quantity to be measured pass throughthe coils, which generate a composite magnetic field. The movablepermanent magnet having a needle is rotated due to the generatedcomposite magnetic field. The known cross-coil moving magnet measuringinstruments have a core, which is used as winding form and within whichthe moving magnets are rotable supported. From one end of the core anextension protrudes, in which the shaft of the moving magnet ispositioned, the magnet receiving the indicating device, which isextended out of said extension. Although, such known cross-coilinstruments are linear to some degree, they fail in applications, wherehighly linear and accurate display is required. In applications, wherethe angles of its deflexion are greater than 90°, the calibration in onequadrant of the instrument can counteract the calibration in otherquadrants of the instruments. Such calibration problems can make itdifficult to achieve linearity. In other applications it would bedesirable to have a highly un-linear characteristic. That would be thecase, when the instrument has to show low values with high resolutionand higher values with a low resolution. There is no easy way to changethe characteristic of the known cross-coil instrument.

It is therefore the object of the invention to provide a cross-coilinstrument with a characteristic which can be predefined. Such aninstrument would be capable to receive an electrical input value andvisually display that value with a predefined angle of deflexion.

SUMMARY OF THE INVENTION

This object is achieved by a cross-coil instrument comprising a driverfor the instrument characterized in that it further comprises a digitalin-put terminal, a predefined characteristic of the instrument stored asa map of input/output values in a digital memory and semiconductor basedlogic, the input value being a value represented visually by thecross-coil instrument, said output value being the value applied to thecross-coil instrument to visually represent the input value. In thisapplication, the term microprocessor is used as a generic term forsemiconductor logic. The map of input/output values in the digitalmemory is a number of calibration points which are used by themicroprocessor to change the input value to a new value which is led tothe driver of the instrument. If the value is not in the digital memory,the microprocessor interpolates the new value from two existingcalibration points on either side of the actual value.

The present invention relates to the visual representation of an inputvalue, and provides an instrument, which can be given any predefinedcharacteristic of its visual display. The instrument of this inventionrelies on an already calibrated input value, but it is also possible toprovide the instrument with additional features known to a man skilledin the art to calibrate an input value, for example a value receivedfrom a sensor.

The use of the present invention gives the possibility of using alow-cost cross-coil instrument while still achieving a high linearity oranother predefined characteristic of the instrument. Furthermore, theuse of the present invention makes it possible to use a heavy indicatingdevice, which is less vulnerable to static electricity and vibrations.When the instrument is manufactured the calibration point can be adaptedto the specific cross-coil instrument used or to the specific type ofcross-coil instruments used. The use of a digital input terminal enablespossibilities for several bus protocols, for instance CAN Bus, NMEA Busor MOD Bus.

In a further embodiment of the invention said semiconductor based logicis selected from the group of semiconductor based logic comprisingmicroprocessor, microcontroller, Field Programmable Gate Array (FPGA),rom, prom, pic, dsp. The choice of the type of semiconductor based logicdepends on the need for speed and other features such as the possibilityto program the logic while it is mounted on the print.

In another embodiment of the invention the predefined characteristic islinear.

In a further embodiment of the invention the predefined characteristicis non-linear, such that the output scale of the instrument isnon-linear. This is advantageous, if it is necessary to have highresolutions in some part of the scale and lower resolutions in otherparts of the scale. This could be the case, when it is needed to readthe frequencies near 50 and 60 Hz with high accuracity, while thefrequency in between said frequencies only need to be read with a loweraccuracity.

In a still further embodiment of the invention cross-coil instrumentcomprises an analogue input terminal and an analogue to digitalconverter. The converter is connected between the analogue inputterminal and the digital input terminal. The use of this embodiment ofthe invention makes it possible to connect the instrument directly to ananalogue signal.

In another embodiment of the invention the instrument is illuminated andthe microprocessor comprising means for dimming the illumination of theinstrument. In some applications, for instance on a bridge on a ship, itis necessary to change the illumination of the instrument, when theambient illumination changes. At night time it is necessary to lower theillumination of the instrument to keep the night view of the people onthe bridge.

In another embodiment of the invention an indication device of saidinstrument is able rotate more than 360°. This is especially useful inpropeller position indicators in a ship with rotating drive systems orin various instruments in trains.

The use of a microprocessor in the instrument makes it possible to addfunctionality to the instrument with low-costs. In a further embodimentof the invention, the instrument is provided with means forerror-detection, means for indication of error, means for test-routinesor error-correcting means, such as offset-adjustment orself-calibration.

For example, the microprocessor can measure the current to the wires ofthe cross-coil instrument. If the current does not have the expectedsize, the microprocessor indicates that using the means for indicationof error. The processor can also detect invalid input, for example amissing input. The instrument can also be provided with anotherprocessor, which acts as watch-dog. In this case the firstmicroprocessor has to send a signal at regular intervals that indicatesthat everything is functioning. If the watch-dog does not receive theexpected signal, it can signal an error. The means for indication oferror can be a sound or light-signal in the instrument. The signal canalso be sent on the digital interface so it can be handled by anexternal system or the cross-coil instrument itself can be used. In thelatter case, an error will be easily detectable if the indication devicemoves in a specific error-pattern, for example slowly from side to sidelike the washers of a car.

The means for test-routines can ensure the user, that the instrument iscalibrated correctly by moving the indicating device to a number ofpredefined positions when the test-routines are running, for example onpower-up or when a run of test-routine is requested manually. The usercan then validate, that the instrument is correct calibrated andeventually initiate the calibration of the instrument.

The error-correcting means can comprise a disc mounted on the cross-coilinstrument in such a way, that it rotates together with the indicatingdevice. Alternatively, the disc can be identical with the indicatingdevice. The disc is provided with a number of holes. An LED andlight-sensor is provided to detect when a hole is positioned between theLED and light-sensor. By using this information, the microprocessor cancontrol the position of the indicating device on a number of predefinedpositions. This information can be used to recalibrate the instrumentautomatically or on request from the user. The microprocessor can alsouse the information to decide, if the indication device is not moved atall. If that is the case, the microprocessor can try to unfreeze theindicating device, for example by using a large current for a shorttime.

In a still further embodiment of the invention the background of theinstrument comprises a liquid crystal display (LCD). The LCD can be usedto change the scale. This could be necessary, if measuring units ischanged. The use of LCD makes it also possible to get a digital readouttogether with the analog readout from the indicating device.

The invention also discloses a method which is particular in that itchanges the characteristic of a cross-coil instrument by reading aninput value and calculates a new value by means of calibration pointsstored in digital memory and applying the new value to the driver of thecross-coil instrument. The calibration points stored in digital memorycan be specific for the specific type of cross-coil instrument used orspecific for the individual cross-coil instrument used. The process ofreading an input value and calculate a new value can be done bysemiconductor logic, such as a microprocessor, microcontroller, FieldProgrammable Gate Array (FPGA), rom, prom, pic or dsp. The calibrationpoints are used to obtain a predefined characteristic of the visualdisplay of the instrument. The calibration points map input values,which are represented visually by the instrument to output values whichare applied to the cross coil instrument to obtain the requireddeflexion of the instrument.

The invention also discloses a method which is particular in that itdetermines a map of input/output values of an digital memory of across-coil instrument comprising the steps of selecting a number ofinput values and their desired, corresponding angles of the instrument,for each pair of input values and desired, corresponding anglesadjusting the input value of the instrument, until the desired angle isobtained, selecting the value which should correspond to the actualangle as the input value of the map, selecting the input value as theoutput value of the map. This method can be applied to every singleindividual manufactured instrument, so that the map is specific forevery single cross-coil, or the method can be applied to an average of aspecific type of cross-coil instrument. The latter application is lessexpensive, and useful when it is known that the characteristic ofdifferent individual cross-coil instrument of a specific type does notdiffer much from each other. This could be the case, where a largeseries of instruments are produced on the same machines.

The invention also discloses a method which is particular in that itcomprises the step of using a camera to detect when the desired angle isobtained. The use of a camera can reduce the costs of the calibration,because the calibration can be done automatic at production time onevery single instrument.

The invention is described by way of example only with reference to theaccompanying drawings, in which

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the invention,

FIG. 2 represents a map of input/output values,

FIG. 3 shows another map of input/output values.

FIG. 4 shows a map of input/output together with direction of movement,

FIG. 5 shows a schematic of a part of one embodiment of the invention,

FIG. 6 shows another map of input/output values comprising both angleand amplitude.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the block diagram of the invention shown in FIG. 1 the digital inputterminal 1 is connected to the microprocessor 2. The microprocessor isconnected to the memory 3, which contains the map of input/output valuesbeing used by the microprocessor to manipulate the input value fromterminal 1, before it is led to the driver 4. The driver 4 drives thecross-coil instrument 5. The driver 4 converts the signal received fromthe microprocessor 2 to analog signals with a different phase. The anglebetween the different signals ideally results in a positioning of theindicating device of the cross-coil instrument in the same angle. Thecross-coil instrument 5 can be of different types. For instance, theindicating device of the instrument can be able to rotate 90, 240, ormore than 360 degrees. Since the cross-coil instrument 5 not is perfect,the angle of the indicating device is not always the same as the anglebetween the signals received from the driver 4. The digital inputterminal can for example be serial, parallel, a microprocessor or abus-system. The microprocessor 2 can be any semiconductor based logic,for example FPGA, PROM, simple logic from the 4000 family, a PIC, amicrocontroller, or a DSP depending on for example the need of speed forthe processor, the price or the complexity of other functions of themicroprocessor. The memory 3 can be volatile or non-volatile and must belarge enough to contain the map of input/output values necessary toachieve the predefined characteristic of the instrument. It isadvantageous that it is possible to program the memory when the memoryis mounted on the print. This is for example possible when the memory isintegrated in a PIC or a microcontroller.

One embodiment of the invention is provided with an analog to digitalconverter 7 and an analog input terminal 6. With an analog inputterminal 6 it is possible to connect the instrument directly to analogsources. An optional digital interface 101 provides means forcommunicating the readout of the instrument or other information fromthe instrument, for example the content of the memory 3 to otheraccessories on a bus-system, for instance CAN Bus, MOD Bus, NMEA Bus ora serial bus-system. The optional digital interface 101 can also be usedfor the initial or any later calibration or validation. The possibilityto read out information from the instrument can be advantageous, if theinstrument is found to be out of calibration. The information can beused to trace an error or to get information on how the cross-coilinstrument changes its physical behavior over time.

Optional means for controlling the illumination of the instrument isprovided with a digital input terminal 106 which receives a controlsignal for the illumination together with the driver 103 which drivesthe illumination of the instrument. The system can be extended with ananalog to digital converter 102 and an analog input terminal 105 toreceive an analog control signal for the illumination 104.

FIG. 2 shows a map of input/output values which are used to achieve apre-defined display of a specific cross-coil instrument. The value,which should be represented visually by the instrument, is located inthe second column 20. This is the input value received from a source,which could be a sensor. The output values are the values in the firstcolumn 21. It is the values which are necessary to apply to thecross-coil instrument to obtain that the cross-coil instrument visuallyrepresent the corresponding value in the second column 20. When theprocessor 2 receives an input value, for example 154, it will look upthe value in the table in the input column 20, and then output thecorresponding output value from the output column 21, which in this caseis 157.5. If the input value is not in the table the processor will makean interpolation to achieve an output signal. This interpolation can belinear, exponential, sinusodial, or another function.

In FIG. 3 the input values are represented by a circle 10. The outputvalue is shown by the curve 11. When a point 13 on the input valuecircle 10 has to be displayed, the curve 11 of output values has acorresponding point 13′, which represents the value, which has to beapplied to the displaying cross coil instrument through the driver for acorrect display of the indicating device of the cross coil instrument.Because the space of the memory is limited the output values arerestricted to the points 13 and 13′. Even though memory is limited, itis also cheap, so there can exist a very high number of points if it isnecessary to obtain the required precision of the visual representation.The curve 12 shows the interpolated output values, which of course willbecome better, when more points are used.

In FIG. 4 the map is extended by an extra set of output values 22. Theuse of such an extended map is useful, when the instrument react indifferent ways with respect to the direction of movement of theindicating device. In one embodiment of the invention, the processorcomprises means for determining the direction of movement of theindicating device, and calculates output values based on one set ofoutput values 20 for one direction and another set of output values 22for another direction.

In FIG. 5 a diagram shows a cross-coil instrument 5 connected to thedriver 4. The microprocessor 2 is a PIC with integrated memory analogterminal 6 with analog to digital converter. A list with the usedcomponents is below.

Bill of Materials Item Quantity Reference Part 1 8 CX1, C1, CX2, C2, C3,C4, C5, 100 nF C6 2 1 C7 10 uF 3 1 C8 470 pF 4 2 C9, C10 10 pF 5 2 C12,C11 22 uF 6 2 C13, C14 47 uF 7 1 D1 SMBJ33CA 8 1 D2 LM336-2.5V 9 1 MG1XCOIL 10 1 N1 TLE2064 11 1 N2 TLE2062 12 1 N3 TL062 13 2 R1, R5 2K40 142 R2, R6 1K00 15 11 R3, R7, R9, R11, R12, R13, R14 20K0 R16, R18, R19,R21 16 2 R4, R8 100R 17 2 R10, R15 2K00 18 2 R17, R20 250R 19 1 T1RM5-24V 20 1 U1 PIC16F873 21 4 U2, U3, U4, U5 1N4148 22 5 U6, U7, U8,U9, U10 BYD77G 23 1 X1 LDG-A-30 24 1 Y1 16MHz

To ensure that the correct force is applied to the indicating device ofthe cross-coil instrument, a further embodiment of the invention isprovided. This embodiment takes into account that a cross-coilinstrument has unlinearities regarding the angle of the indicatingdevice and that different strength of signal has to be applied todifferent cross coil instruments at different angles to provide that theindicating device is held at a given angle with a given force. In thisembodiment, the input/output values are vectors, so that the driver canobtain the necessary information to provide the correct signal to theinstrument.

An example is shown FIG. 6, where a limited number of input values 10′is represented located on a perfect circle 10. In this figure, thediameter of the circle represents the force, which should maintain theindicating device on the correct position, and the angle as the value,which should be represented visually by the indicating device of thecross-coil instrument. The output values 15′ located on the curve 11correspond to the input values 15. Both the input value points 15 andthe output value points 15′ are vectors. This map can be used to adjustboth the angle and the amplitude of the input value before it is appliedto cross coil instrument through the driver. For example, for this givenmap, the output vector 16′ has to be applied to the cross coilinstrument, when the input value vector 16 has to be representedvisually by the indicating device. The microprocessor adjusts the inputwith respect to angle as well as amplitude. In this embodiment, thedriver used uses both the angle and the amplitude as input. Because thespace of the memory is limited the output values are restricted to thepoints 15′, and the number of input values are restricted to the points15. Even though memory is limited, it is also cheap, so there can exista very high number of points if it is necessary to obtain the requiredprecision of the visual representation. The curve 12 shows theinterpolated output values, which of course will become better, whenmore points are used.

1. Cross-coil instrument comprising a driver for the instrument whereinit further comprises a digital input terminal a predeterminedcharacteristic of the instrument stored as a map of input/output valuesin a digital memory semiconductor based logic, said input value being avalue represented visually by the cross-coil instrument, said outputvalue being the value applied to the cross-coil instrument to visuallyrepresent the input value.
 2. Cross-coil instrument according to claim1, where said semiconductor based logic is selected from the group ofsemiconductor based logic consisting of microprocessor, microcontroller,Field Programmable Gate Array (FPGA), rom, prom, pic, and dsp. 3.Cross-coil instrument according to claim 1, where said characteristic islinear.
 4. Cross-coil instrument according to claim 1 where saidcharacteristic is non-linear, such that the output scale is non-linear.5. Cross-coil instrument according to claim 1 comprising an analogueinput terminal, an analogue to digital converter connected to theanalogue input terminal and the digital input terminal.
 6. Cross-coilinstrument according to claim 1 where the indicating device of saidinstrument is able to rotate more than 360 degrees.
 7. Cross-coilinstrument according to claim 1 where said instrument is illuminated andoptionally the semiconductor based logic comprising means for dimmingthe illumination of the instrument.
 8. Method of obtaining a predefinedcharacteristic of a cross-coil instrument comprising the step of read aninput value by semiconductor based logic, calculate a new value by usingthe input value and information in a digital memory which represent saidpredefined characteristic, use said new value as the input signal to thedriver of said cross-coil instrument.
 9. Method according to claim 8,wherein said semiconductor based logic is selected from the group ofsemiconductor based logic consisting of microprocessor, microcontroller,Field Programmable Gate Array (FPGA), rom, prom, pic and dsp.
 10. Methodof changing the characteristic of a cross-coil instrument comprising thesteps of read an input value calculate a new value by means ofcalibration points stored in digital memory apply the new value to thedriver of the cross-coil instrument.
 11. Method of determining a map ofinput/output values storing input/output values in a digital memory of across-coil instrument comprising the steps of defining a number of inputvalues and their desired, corresponding angles of the instrument, andfor each pair of input values and desired, corresponding angles adjustthe input value of the instrument, until the desired angle is obtained,selecting the value which should correspond to the actual angle as theinput value of the map, selecting the input value as the output value ofthe map.
 12. Method of determining a map of input/output values of adigital memory of a cross-coil instrument comprising the steps ofselecting a number of input values and their desired, correspondingangles of the instrument, and for each pair of input values and desired,corresponding angles adjusting the input value of the instrument, untilthe desired angle is obtained, selecting the value which shouldcorrespond to the actual angle as the input value of the map, selectingthe input value as the output value of the map, further comprising thestep of using a camera to detect when the desired angle is obtained.